PSP injury

I've been playing Puzzle Quest on my PSP more than usual lately, great game, but unfortunately I am developing some thumb pain. Specifically at my left metacarpophalangeal joint (MCP) (the hand I use on the D-pad). Have some crossover symptoms when I cook and drive, or picking up a heavy object where I have to stabilize with the thumb (like a laptop). I guess I'm going to have to cut back for a little while, may or may not use a splint for a bit. Curiously I played some Super Mario Galaxy, holding the Nunchuck with my left, didn't seem to bother me much.